The present invention relates to a method of manufacturing a magnetic recording medium, particularly of thin metallic film type.
Instead of magnetic recording media of coating type, attention is now being paid to a magnetic recording medium of thin metallic film type which has high magnetic coercive force and high residual flux density. The magnetic recording medium of thin metallic film type is usually made by forming a thin metallic magnetic film layer directly on a plastic base film by means of vacuum evaporation. Because of strong internal stress left in the thin metallic film at the time of vacuum evaporation, however, the magnetic recording medium is warped making the side of its magnetic layer concave. With a magnetic medium such as magnetic tape, when there is a warp, the running capacity worsens, its winding order is disturbed and it can not be used with a magnetic recording medium such as magnetic sheet.
In order to prevent warps in the magnetic recording medium of thin metallic film type, cracks are provided in the magnetic layer, nearly parallel to its recording direction. When such cracks are provided in the magnetic layer, the internal stress left in the width direction of magnetic layer, that is, in a direction perpendicular to the recording direction of magnetic layer is reduced to give flexibility to the magnetic recording medium as well as to prevent the magnetic recording medium from being warped. The running capacity of magnetic recording medium of thin metallic film type can be thus improved remarkably. A well-known method of manufacturing this thin metallic film type of magnetic recording medium is disclosed by Japanese Patent Disclosure No. 53/83706 in which a thin metallic film type of magnetic recording medium is passed between a convex roller and a concave roller to form cracks on its magnetic layer. This method, however, needs special mechanical units such as convex and concave rollers, thus increasing the cost of manufacturing recording media.